1. Field of the Invention
The present invention relates to a resistor-capacitor (RC) oscillation circuit capable of adjusting an oscillation frequency and an oscillation method thereof, and more particularly, to an RC oscillation circuit capable of adjusting an oscillation frequency in which a resistance of a variable resistor and a capacitance of a variable capacitor are determined to control an oscillation frequency promptly and accurately despite changes in operating environment such as temperature, and an oscillation method thereof.
2. Description of the Related Art
In 2000, the Institute of Electrical and Electronics Engineers (IEEE) launched a move to standardize a low-speed wireless private network application into IEEE 802.15.4. This standardized version requires a battery to run for at least 5 to 7 years, which thus necessitates designing of a circuit consuming minimal power. The most widely known technology for minimizing power consumption is to turn off a circuit when it does not need to be in operation.
Meanwhile, in a system where a power is turned off during deactivation for less power consumption, the power should be turned on and off through a shorter time to reduce power consumption of the system. Especially, this characteristic is notably important in an oscillator circuit for generating a reference frequency which is essentially used in a telecommunication system.
In general, a conventional crystal oscillator needs time for self-start to amplify noises generated internally to an operational level. Accordingly, the conventional crystal oscillator entails a long operation time and significant power consumption to start oscillating. In consequence, the crystal oscillator with such operation time and power consumption is ill-suitable for a system which has a power turned off during deactivation to minimize power consumption.
To overcome problems with the conventional crystal oscillator, a resistor-capacitor (RC) oscillator has been suggested. The RC oscillator is inexpensive, low in power consumption, short in starting time and easily controllable in a frequency. Also, the RC oscillator may be included in a system-on-a-chip so that a telecommunication system may be implemented as one chip.
FIG. 1 is a block diagram illustrating a configuration of a conventional RC oscillation circuit. As shown in FIG. 1, the conventional RC oscillation circuit includes a phase frequency detector (PFD) 11, a low pass filter (LPF) 12, a voltage holder (VH) 13 and a voltage control oscillator, i.e., an RC oscillator 14.
In a brief description of the conventional RC oscillator, the PFD 11 receives a TXCO clock from a temperature compensator Xtal Oscillator TXCO and an output clock from the voltage control oscillator 14, compares the TCXO clock with the output clock from the voltage control oscillator 14, and outputs a frequency and a phase difference to the low pass filter 12.
The LPF 12 converts a signal outputted from the PFD 11 into a voltage.
The VH 13 maintains a current output voltage when a hold signal is fed from the outside and outputs the voltage from the LPF 12 to the VCO 14 when a pass signal is fed from the outside.
The VCO 14 is configured as the RC oscillator and has an oscillation frequency changed according to an input voltage.
The conventional RC oscillation circuit requires the voltage control oscillator, and may have an oscillation circuit degraded in stability due to a feed back loop formed, and may experience increase in time for adjusting the oscillation frequency.